Peripheral Oxygen Saturation Targets and Hyperoxemia in Critical Care: Influence of pH, F_iO₂, and Respiratory Failure

Oxygen therapy is a cornerstone in the treatment of critically ill patients. However, excess oxygen administration may promote oxidative cellular injury once hemoglobin is fully saturated and additional oxygen remains dissolved, enhancing reactive oxygen species formation. The combined impact of oxygen administration, pH, and respiratory failure on hyperoxemia across saturation ranges is not well understood. We conducted a retrospective study at a tertiary center to assess how these factors modify hyperoxemia frequency in adult ICU patients. Continuous S_pO₂ measurements were aligned with arterial blood gases (P_aO₂, pH, F_iO₂), and hyperoxemia was evaluated using predefined P_aO₂ thresholds (>120 mmHg and >150 mmHg). Among 21,406 patients with 717,064 paired measurements, prolonged hyperoxemia occurred in over half of mechanically ventilated patients, most commonly in those without or with mild-to-moderate respiratory failure. Acidotic states were associated with higher P_aO₂ values at comparable S_pO₂ levels, consistent with a rightward shift in the oxygen-hemoglobin dissociation curve. S_pO₂ values ≥ 98% were consistently associated with hyperoxemia, whereas 96-97% generally corresponded to P_aO₂ within physiological ranges. Higher F_iO₂ markedly increased hyperoxemia probability, allowing derivation of pH-stratified F_iO₂ exposure limits. Our findings highlight the importance of individualized oxygen therapy, considering pH and respiratory failure phenotype to guide safer oxygen management.